Conventional internal combustion engines use two different processes, constant volume and constant pressure. The constant volume process is characteristic of spark-ignition engines or the Otto cycle. A spark ignition engine uses volatile liquid fuels such as gasoline, compression ratios from 6:1 to 12:1, and compression pressures from 1034 to 2068 kPa. Engine load and speed are controlled by throttling the fuel charge. The constant pressure process is typified by diesel engines or compression ignition engines. A compression ignition engine uses low volatility liquid fuels from fuel oil to crude oil, compression ratios from 11.5:1 to 22:1, and compression pressures from 2768 to 4830 kPa. Engine load and speed are controlled by varying the fuel quantity injected.
Three general types of arrangements of engines are used, four stroke, two stroke, and rotary or Wankel engines. These engines are typically fixed piston engines. That is, the pistons have a predetermined and constant or fixed stroke. This stroke is set up for the particular type of fuel to be used in the engine. Moreover, the pistons are connected through a connecting rod to a crankshaft in order to convert the combustion energy into mechanical work. The crankshaft in turn is used to drive all of the other systems of the automobile or machine. So, the nature of these engines is to produce net mechanical shaft work.
Numerous innovations for combustion engines have been attempted to improve the efficiency, and hence output or work, of an engine without adding undue cost or size. Engines exist that combine the rotation of a rotary engine with the reciprocation of pistons. For example, U.S. Pat. No. 3,990,406 discloses a roto-reciprocating engine arranged to provide an engine that has a large cubic inch displacement per pound of unit weight and therefore a good horsepower to weight ratio. The engine includes a chamber, a piston in the chamber mounted on a crankshaft, and an orientation member arranged to make it possible for the piston to orbit around the crankshaft center while remaining in a substantially oriented position.
U.S. Pat. No. 5,433,176 discloses a rotary-reciprocal combustion engine. The engine includes a rotor which has circular pistons on the lateral peripheral area of the rotor and which is reciprocatively mounted on a rotor with a shaft centrally located in a fixed housing having a cavity formed by a circular peripheral wall and two sidewalls. The circular pistons or sealing mechanisms or apparatus reciprocate on the peripheral area of the rotor while rotating with the rotor and shaft. U.S. Pat. No. 5,070,825 discloses a rotary engine with a wobble plate and a plurality of pistons reciprocating within cylinders.
U.S. Pat. No. 4,166,438 is directed to a machine with reciprocating pistons and a rotating piston carrier. The engine overcomes sealing deficiencies of rotary engines by using conventional pistons. The engine includes a housing surrounding a workshaft, a carrier in the housing about the shaft and rotatable about the shaft axis, a plurality of continuous walls within the carrier each defining a chamber, and a piston in each chamber connected to a crankshaft where each crankshaft is linked to the housing to induce relative movement between the housing and the carrier. Induced motion of the pistons results in a revolution of throw arms of the cranks, causing motion of the gears with respect to the timing gear, thus imposing rotational motion on the carrier and shaft.
Other engines use a free piston arrangement, wherein the stroke of the piston is not set by attachment to a shaft of predetermined length. U.S. Pat. Nos. 4,399,654, 4,561,252, and 4,702,205 disclose such engines. Further, in these engines, the combusted gas exhaust is used to turn vanes in a motor to produce shaft power. U.S. Pat. No. 3,989,011 discloses a constant pressure heating vane engine. This engine uses a system similar to a gas turbine to generate shaft work.
U.S. Pat. No. 5,327,857 discloses a vehicle using a crankless, unthrottled internal combustion engine directly powering its wheels hydrostatically. The vehicle uses a spark or compression ignited two-cycle type engine, an optional recovery and reuse of a portion of its braking energy, and hydraulic pressure for compression of the air and fuel mixture. U.S. Pat. No. 4,382,748 discloses an opposed piston type free piston engine pump for converting combustion energy into hydraulic power. The motion of the engine is at least substantially directly delivered to hydraulic pumping elements, usually, without crankshaft and connecting rod arrangements of conventional rotary engines. The engine includes a pump piston and engine pistons arranged for linear in-line reciprocation wherein the hydraulic pump portion supplies energy for effecting a compression stroke to bring the engine pistons toward one another thereby to effect compression.